The provision of embedded waveguide structures to provide embedded sensing and/or embedded communications channels provides various known benefits. Where such waveguide structures are provided integrally within, for example, an aircraft, relatively light materials, such as, for example, optical fibres (fibre optics) may be provided, which are not only lighter than traditional metal wiring, but also relatively noise-immune and inexpensive.
While it is desirable to embed waveguide structures within panels that form a larger structure, such as, for example, a building or aircraft it has proved to be reasonably difficult and time consuming to provide reliable connections to such embedded waveguide structures, particularly during the process of manufacturing the larger structure.
Conventionally, to produce a panel, such as a composite panel for an aircraft incorporating an embedded waveguide, a waveguide (such as, for example, a fibre optic) is embedded in the composite panel and emerges from an edge of the panel from where it is terminated into a connector. However, not only are such so-called “edge connectors” labour intensive to produce, but they also place substantial limitations upon any subsequent modification to the panels. This in turn means that it has been necessary to provide a range of different panels in different shapes and sizes to assemble into the larger structure. This not only increased the tooling costs and complexity involved in producing a complex larger structure, but also gave rise to a requirement for intensive use of skilled labour capable of making the edge connectors.
In order to address the problems associated with panels using edge connectors, and in particular in order to provide a panel that could be shaped after manufacture to allow, for example, for the removal of peripheral defects, the Applicants have previously devised various ways of interfacing to embedded waveguides. Various methods are discussed further in the present Applicant's patent applications EP-A1-1,150,145 and EP-A1-1,150,150, the contents of which are hereby incorporated herein by reference in their entirety.
The aforementioned patent applications describe various ways of interfacing optical fibres, incorporated into components made using composite materials, to surface-mountable interface modules. The optical fibres are accessed from the surface of the components post-manufacture in order to leave the surface of the components free of incisions, cavities and the like during the assembly of various components into a larger structure, such as, for example, an aircraft body.
While embedding of optical fibres and various interfacing components within a substrate, such as a composite material, can facilitate assembly of such a larger structure, since waveguide connections can be made post-assembly, this approach is not without certain drawbacks. Processing of the substrate structure to reveal embedded components with which to interface can be quite difficult and time-consuming. This is partly because the components must first be located and then subsequently exposed. Ease of exposure of components may also be hindered as the substrate structure will already be part of the larger structure which may in turn make accessibility an issue when attempting to “dig out” or expose the interface components. Furthermore, the task of exposing the embedded components calls not only for a skilled technician, but also requires the use of specialist equipment.
Another consideration in relation to conventional embedded connector components is that they may need to be non-standard, and thus may require additional manufacturing facilities to produce them. This can increase the relative cost and complexity when compared to standard type waveguide connectors. Moreover, use of such embedded connector components may also result in sub-optimal alignment, finishing, polishing, etc., thereby leading to relatively high insertion and/or coupling losses. For example, certain conventional connectors use tubing to reinforce an exit point of a waveguide from a composite material. Not only does this damage the composite since the fibres must be teased apart, but it is also very labour intensive and therefore sub-optimal for manufacturing.
Additionally it is generally undesirable, post-assembly into a larger structure, to use complex processing of fibre optic components either near to the edges or the centre of the substrate to produce a suitable connector, since this increases the chance of weakening the fibre optics and/or their support structures and also may mean that they become damaged, possibly resulting in a need for their subsequent removal and replacement. Moreover, waveguide connectors produced by processing exposed fibre optic components post-assembly cannot be tested until they have been formed, thereby introducing a risk that a panel including a defective connector be included in the larger structure. This could in turn require subsequent remedial attention, like replacement of a section of structure, such as, for example, a full aircraft panel, despite the expenditure of the time and effort to produce the defective connector.
Various techniques relating to the use of fibre optic components and/or embedding of fibre optic components into substrate structures may also be found in the following documents, the teachings of all of which are hereby incorporated herein by reference in their entirety: “Termination and connection methods for optical fibres embedded in aerospace composite components,” A. K. Green and E. Shafir, Smart Materials and Structures, Volume 8(2), pp. 269-273 (1999); “Optical fiber sensors for spacecraft applications,” E. J. Friebele et al, Smart Materials and Structures, Volume 8(6), pp. 813-838 (1999), which discloses use of a rubber tool attached to the surface of a composite material after it is cured; “Development of fibre optic ingress/egress methods for smart composite structures,” H. K. Kang et al, Smart Materials and Structures, Volume 9(2), pp. 149-156 (2000); “Infrastructure development for incorporating fibre-optic sensors in composite materials,” A. K. Green et al, Smart Materials and Structures, Volume 9(3), pp. 316-321 (2000); and “Manufacturing technique for embedding detachable fiber-optic connections in aircraft composite components,” A. Sjögren, Smart Materials and Structures, Volume 9(6), pp. 855-858 (2000).
The aforementioned considerations and documents have been borne in mind when devising the various aspects and embodiments of the invention, as herein described.